The production and use of sheets of cellulose-based paper that are impregnated with surfactants and are wholly water-soluble are known. However the terminology used for the substrate or the final product, paper or tissue, is not always uniform and is sometimes a source of confusion and misunderstandings.
In the paper industry, by paper is meant a felt of vegetable fibres whose main components are cellulose and lignin, obtained from a suspension of such fibres in water. Conversion from a suspension to felt is achieved through draining on a clothing. The thin sheet so obtained has magnitudes in two dimensions, width and length, which are many orders greater than the third, its thickness.
In the meaning of this invention, by paper is meant a product containing at least 50% of cellulose or cellulose and lignin. In the meaning of this invention known products having a lower percentage are not regarded as being paper. GB656210 describes a tissue which can be used as a substitute for soap formed of water-soluble cellulose ether fibres and surfactants (e.g. alkyl sulphates) which may contain the sodium salt of carboxymethylcellulose as the binding agent between the fibres. The process of producing the substrate known as “tissue” may be obtained using paper production technology, but the starting material comprises cellulose ethers. The tissue is therefore obtained by forming a pulp of cellulose ether fibres in a liquid which also contains surfactants; this pulp is then spread onto a forming grid to form a “feltrate” layer from which the liquid is drained and the remaining liquid is removed by evaporation. The starting material used to obtain the tissue to which the patent relates is always a water-soluble fibrous material, preferably a cellulose ether or alternately an alginate or polyvinyl alcohol. In the patent cellulose is only cited as the starting material (reagent) in order to obtain the methyl cellulose. Thus the material used to form the substrate (cellulose ethers) differs from cellulose. The product described cannot be regarded as paper, in that the starting material does not provide at least 50% of cellulose or cellulose and lignin.
EP0003186 describes wet wipes of high mechanical strength obtained by adding a binding agent, polyvinyl alcohol (PVA, PVOH), to a substrate described as “non-woven fabric” (which by definition is different from paper because in non-woven fabric dimensional stability is imparted by a polymer matrix and not by the inter-fibre hydrogen bonds of cellulose). The substrate containing PVA must subsequently be treated with products (boric acid and water-soluble salts) to ensure that the material so obtained (wipes) is dimensionally stable when placed in contact with water. The wipes have good resistance to moisture but break up (disaggregate) when immersed in water and subjected to agitation. In the examples it is learnt how the required mechanical strength is only obtained after the paper has been processed with polyvinyl alcohol and boric acid. In addition to this, disaggregation is accomplished only by providing a certain amount of external energy, in particular mechanical energy.
EP0896089 describes substantially the same product as EP0003186, but with greater accuracy and precision, and with some changes in the formulation of the products added to the substrate. In this case explicit reference is made to paper (fibrous sheet such as paper) to which is added a binding agent (binder), polyvinyl alcohol (PVA), through surface treatment. Subsequently a carboxylate is added to the paper containing PVA to impart sufficient strength to the sheet for it to be rubbed even when it is soaked. In the description a disintegration time for the wipe is quantified through a test which provides for the use of a rotor at increasing rotation speed. Disintegration of the wipe in water therefore requires the application of a certain amount of energy.
CA233748 describes a disposable soap comprising a substrate dissolving in water which is impregnated with a cleansing composition placed in a container. This substrate may be a tissue, and paper is understood to be the material. This reference only describes individual sheets (wipes). The possibility of producing a roll is never mentioned.
WO2005060931 describes cleansing wipes formed of a single layer which dissolve in contact with water, comprising a polymer material forming a water-soluble film (70-98%) containing materials which are soluble and/or dispersible in water, and a cleansing agent (1-30%). They may also possibly contain an abrasive cleansing agent or a fibrous filler which may comprise wood fibre, therefore also cellulose, in quantities from 1 to 20%. Cellulose is not mentioned among the materials which can be dispersed in water. An essential feature of the product described is its suitable wet strength which enables it to maintain an intact structure for a sufficient time for cleansing.
In the documents of the state of the art described above there are therefore descriptions of wipes or tissues with good wet strength that are capable of sustaining a rubbing action against the skin. These disintegrate when they are subjected to a high flow of water but in the additional presence of significant mechanical action providing energy.
Furthermore the products described in documents GB656210 and WO2005060931 do not fall within the scope of the conventional definition of “paper” because the latter provides for the presence of vegetable fibre, the main components of which are cellulose or cellulose and lignin in a quantity in excess of 50%.
JP2003082397 and JP2003073700 describe a water-soluble soaped paper comprising an alkaline salt of carboxymethylcellulose (CMC) and wood pulp. However as in the case of documents GB656210 and WO2005060931 these products do not fall within the scope of the conventional definition of “paper” because the latter provides for the presence of vegetable fibre, the main components of which are cellulose or cellulose and lignin, in a quantity in excess of 50%.
JP2003082397 also provides for the presence of a component which retains moisture. The paper is obtained by mixing carboxymethylcellulose and wood pulp in proportions of approximately 75-85 and 15-25 respectively, and drying. The soluble paper is then coated with liquid soap and dried by heat.
One of the essential features of the soaped soluble paper described in the abovementioned Japanese patents is that they are wholly soluble in water.
The present inventors are aware of a soaped paper which will disaggregate in water, which is prepared by hand by craft means. The craft production cycle provides for placing a solution of water and cellulose fibres in a vessel (FIG. 1a) which deposits out through gravity onto a forming cloth; this forming cloth is subsequently lifted from the water, draining off a good part of the excess water. A cellulose paste remains on the forming cloth (FIG. 1b) and is subsequently spread out (FIG. 1c), manually impregnated with soap solution, dried by means of hot air jets and finally rolled up. This process carried out on a craft basis makes it possible to produce limited quantities of soaped paper. Because of its intrinsic characteristics and small dimensions the soaped paper sheet obtained cannot be rolled up and is therefore cut into small pieces which are subsequently stacked (FIGS. 1d, 1e, 1f and 1g). The small sizes of the hand-made product (individual sheets) so obtained will not allow it to be produced industrially in rolls of desired length and width. This is an impediment to its storage and automatic production on an industrial scale.
An industrial process for obtaining soluble paper which can be wound into rolls is known and implemented by the Aquasol company (Aquasol Corporation, 80 Thompson Street/North Tonawanda, N.Y. 14120). The company produces Aquasol® Water Soluble Paper, a soluble paper characterised by the property that it can quickly disaggregate in water and is available in a variety of thicknesses and sizes, including rolls and sheets. This soluble paper is not however soaped, neither is it impregnated with any substance.
In the light of the state of the art described above there is still a need for a process that makes it possible to obtain a completely water-soluble soaped paper which can be made available in various formats, in particular in the form of a roll, produced through a continuous industrial process.